The approach to landing and touch down on the runway of an aircraft is one of the most challenging tasks a pilot undertakes during normal aircraft operations. To perform the landing properly, the aircraft approaches the runway within an envelope of attitude, course, speed, and rate of descent limits. The course limits include, for example, both lateral limits and glide slope limits. An approach outside of this envelope can result in an undesirable positioning of the aircraft with respect to the runway, resulting in a possible discontinuance of the landing attempt.
In some instances visibility may be poor during approach and landing operations, resulting in what is known as instrument flight conditions. During instrument flight conditions, pilots rely on instruments, rather than visual references, to navigate the aircraft. Even during good weather conditions, pilots typically rely on instruments to some extent during the approach. Many airports and aircraft include runway assistance landing systems, such as an Instrument Landing System (ILS), to help guide aircraft during approach and landing operations. The ILS allows a lateral deviation indicator to indicate aircraft lateral deviation from the approach course, and a glide slope indicator to indicate vertical deviation from the glide slope.
A conventional ILS includes a localizer subsystem and a glide slope subsystem. The localizer subsystem includes a localizer antenna array that radiates an RF carrier signal that is amplitude modulated with equal amplitudes of 90 Hz and 150 Hz tones. A localizer receiver onboard an aircraft demodulates these signals and drives the lateral deviation indicator. The glide slope subsystem includes a glide slope antenna array that radiates an RF carrier signal that is also amplitude modulated with equal amplitudes of 90 Hz and 150 Hz tones. A glide slope receiver on-board the aircraft demodulates these signals and drives the glide slope indicator.
Though rare, there have been instances where an aircraft is taking off from the same runway that an aircraft is about to land, and temporarily interferes with the ILS signals. This temporary interference can cause the ILS signals to be imbalanced. If the imbalance is of a sufficient duration, it can cause the aircraft flight control/autopilot system to undergo and unneeded and undesirable maneuver. In one particular documented case, the undesirable maneuver caused the aircraft to land on the left main landing gear only. The different forces caused the aircraft to temporarily slide off the runway. This incident, and future incidents, may be avoided if the crew is provided with an on-board ILS signal monitoring function that will alert the crew that an automatically determined maneuver is not compatible with the actual intended course direction. Presently, no such function is provided.
Hence, there is a need for a system and method that will alert the crew that an automatically determined maneuver, based on received ILS signals, is not compatible with the actual intended course direction. The present invention addresses at least this need.